fix(aws-codepipeline): update CFN example. (#1653)

This test is referred as example in the
[Cloudformation README](https://github.com/awslabs/aws-cdk/blob/master/packages/%40aws-cdk/aws-cloudformation/README.md).
But the example doesn't do what it intended.
Without specifying the runOrder the `pipelineExecuteChangeSetAction` will be triggered immediately without change set being populated,
which will lead to deployment failure.
After adding the `runOrder` the 3 actions will run in order and only be deployed after manual approval.

Author: AllanZhengYP

packages/@aws-cdk/aws-codepipeline/test/integ.cfn-template-from-repo.lit.expected.json

@@ -247,7 +247,7 @@
                 "InputArtifacts": [],
                 "Name": "ApproveChanges",
                 "OutputArtifacts": [],
-                "RunOrder": 1
+                "RunOrder": 2
               },
               {
                 "ActionTypeId": {
@@ -264,7 +264,7 @@
                 "InputArtifacts": [],
                 "Name": "ExecuteChanges",
                 "OutputArtifacts": [],
-                "RunOrder": 1
+                "RunOrder": 3
               }
             ],
             "Name": "Deploy"

packages/@aws-cdk/aws-codepipeline/test/integ.cfn-template-from-repo.lit.ts

@@ -35,12 +35,17 @@ const prodStage = {
       changeSetName,
       adminPermissions: true,
       templatePath: source.outputArtifact.atPath('template.yaml'),
+      runOrder: 1,
+    }),
+    new codepipeline.ManualApprovalAction({
+      actionName: 'ApproveChanges',
+      runOrder: 2,
     }),
-    new codepipeline.ManualApprovalAction({ actionName: 'ApproveChanges' }),
     new cfn.PipelineExecuteChangeSetAction({
       actionName: 'ExecuteChanges',
       stackName,
       changeSetName,
+      runOrder: 3,
     }),
   ],
 };